When two or more networks are connected,they become an internetwork or internet.Individual networks are joined into internetworks by the use of internetworking devices.These devices,which include routers and gateways are discussed in details in the internetworking devices category.
The term internet(lowercase i) should not be confused with the Internet(uppercase I).The first term used to mean an interconnection of networks.The second is the name of a specific worldwide network.

A typical diagram if INTERNETWORK is shown in the figure below:-